Trust has nothing to do with it. Based on seroprevalence studies and other factors the CDC has estimated that only about a quarter of infections were officially counted as "cases". The undercounting was even worse early in the pandemic when tests were hardly available. So your point is not valid.

https://www.cdc.gov/coronavirus/2019-ncov/cases-updates/burd...

But that's US statistics, this happened in asmall area in Northern Italy.

Even if we go with your numbers, we get an average of 4-5% and since we know there was a huge spike in the middle of the outbreak it is not unrealistic to assume they were above 10% at some point.